The present invention pertains generally to fluid dispensers and related apparatus used to produce on-demand foam-in-place packaging cushions and, more particularly, to an improved system for delivering cleaning solvent to certain portions of such fluid dispensers that are particularly susceptible to occlusion due to build-up and/or hardening of fluid within the dispenser.
The invention finds particularly utility in the field of foam-in-place packaging, which is a highly useful technique for on-demand protection of packaged objects. In its most basic form, foam-in-place packaging comprises injecting foamable compositions from a dispenser into a container that holds an object to be cushioned. Typically, the object is wrapped in plastic to keep it from direct contact with the rising (expanding) foam. As the foam rises, it expands into the remaining space between the object and its container (e.g. a corrugated board box) thus forming a custom cushion for the object.
A common foamable composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure, i.e., a polyurethane foam, which serves to protect the packaged object.
In other types of foam-in-place packaging, an automated device produces flexible containers, e.g., in the form of bags, from flexible, plastic film and dispenses a foamable composition into the containers as the containers are being formed. As the composition expands into a foam within the container, the container is sealed shut and typically dropped into a box or carton holding the object to be cushioned. The rising foam again tends to expand into the available space, but does so inside the container. Because the containers are formed of flexible plastic, they form individual custom foam cushions around the packaged objects. Exemplary devices for automatically producing foam-in-place cushions in this manner are assigned to the assignee of the present invention, and are illustrated, for example, in U.S. Pat. Nos. 4,800,708, 4,854,109, 5,376,219, and 6,003,288, the contents of each of which are incorporated entirely herein by reference.
One difficulty with the foamable compositions used to make polyurethane foam for foam-in-place packaging is that the foam precursors and resultant foam tend to have somewhat adhesive properties. As a result, the foamable composition tends to stick to objects and then harden thereon into foam. This tendency is particularly problematic inside of the dispenser from which the foam precursors are ejected. As is known, the polyol and isocyanate foam precursors must be withheld from mixing with one another until just prior to injection. In the most common type of dispenser, the two foam precursors enter the dispenser, mix with one another in an internal chamber disposed within the dispenser to form a foamable composition, and then the resultant foamable composition exits the dispenser via a discharge port. As the dispenser operates over and over again, particularly in automated or successive fashion, foamable composition tends to build up in the internal mixing chamber and around the discharge port of the dispenser, harden into foam, and block the proper exiting of further foamable composition. As a result, the mixing chamber and discharge port must be frequently cleaned to ensure continued operation of the dispenser.
Further, such dispensers generally employ a valving rod that translates longitudinally within the mixing chamber to control the flow of the foam precursors therethrough, i.e., between an ‘open’ position, in which the precursors flow into and through the mixing chamber, and a ‘closed’ position, in which the precursors are prevented from flowing. Such valving rod is in contact with the foam precursors and resultant foamable composition, and thus must also be continually cleaned in order to prevent the build-up of foam thereon, which would otherwise impede and eventually prevent the further movement of the valving rod within the dispenser.
A solvent capable of dissolving both the foam precursors and the foamable composition is typically used to clean the dispensers. In order to clean the dispenser on an on-going basis without the necessity of frequent removal of the dispenser from the cushion-making device for manual cleaning and/or disassembly, solvent is generally contained in a reservoir located behind the mixing chamber and/or supplied to the discharge end of the dispenser from a separate source. Part of the valving rod moves through the reservoir as it translates between open and closed positions to partially clean the valving rod. However, the foam precursors and reaction products thereof gradually contaminate the solvent in the reservoir as they are transferred thereto from the valving rod. This requires periodic removal of the dispenser to either replace it with a dispenser having fresh solvent or to disassemble the cartridge for cleaning and replacement of the solvent. Further, while previous techniques for supplying solvent to the discharge end of the dispenser have been somewhat effective, none has been able to deliver solvent directly against the internal surfaces of the mixing chamber and discharge port.
As a result of the foregoing shortcomings, the effective service life of conventional dispensers has been much shorter than would otherwise be desired. It would therefore be desirable to extend this service life to the greatest extent possible.
Accordingly, a need exists in the art for an improved means for continually and automatically cleaning dispensers used in foam-in-place packaging.